U-shaped extruded elastomeric strips are in general use in the manufacture of automotive vehicles for sealing and decorative purposes. While it will be appreciated that such strips have many uses, such as in the appliance industry, the present invention will be described in the context of the automobile industry where such strips are commonly used to cover flanges which extend around various openings such as are found around doors, trunks and the like. The strips can simply cover the flange, or in many cases, cover the flange and also carry another member such as a sealing member bulb or a fin to cover an associated gap running along the flange.
Generally speaking, the extrusions are made by extruding an elastomeric material about a metallic core which serves to reinforce the legs of the U-shaped extrusion so that the extrusion will effectively secure to an associated flange with sufficient clamping force. Some cores are stamped or lanced from a metal sheet. Other cores are made by winding a wire in surpentine fashion. The present invention especially relates to extrusions made using the wire type of core. Wire core based extrusions are well-suited to provide clamping force in a direction transverse to the extrusion but require additional tensile strength in the longitudinal direction, particularly during the extrusion process when the elastomeric material is not yet cured. The conventional exrusion process involves first extruding the elastomeric material about the core and then pulling the elongated extrudate by primary puller rolls or belts for cooling and further processing steps. Satisfactory extrusion requires that the extruded strip maintain a neutral geometry in the extruder and have tensile strength along its longitudinal axis in order to allow pulling of the strip through curing and cooling steps after the extruder.
One method of providing tensile strength to wire cores is to employ warp threads to knittingly hold adjacent parallel transverse wire segments in spaced relationship. This method deals with the processing limitations imposed by lack of tensile strength but introduces a problem when the extruded strip is applied to the usual curved flange. Flange edges commonly extend around the periphery of openings and are curved. It has been found that application of extrusions with threads rigidly holding the wire core in spaced relationship to a curved flange results in a bending axis which twists an associated seal or fin out of alignment if the extrusion has a neutral geometry. Thus, it has been found desirable to provide some flexibility in the wire to provide the extrusion with assymetric geometry to accommodate use of the extrusion on a curved flange edge.
One method of providing additional support to metal wire core is taught in U.S. Pat. No. 5,416,961 Jan. 26, 1994, to Vinay. The Vinay patent teaches a knitted wire core for use in the manufacture of weather seals comprising, a wire folded into a zigzag configuration for carrying a plurality of polymeric warp threads knitted on the wire and at least one meltable filament laid into at least two adjacent warp threads, whereby on heating, the melted filament causes the at least two adjacent warp threads to be bonded to the wire and/or to each other.
Another patent relating to support frames having longitudinally displaceable frame portions that are reinforced with longitudinally extending degradable reinforcing material is U.S. Pat. No. 5,143,666 Sep. 1, 1992 to McManus et al. The McManus patent involves advancing a reinforced support frame through an extrusion die where a coating of an elastomeric material is extruded on the support frame to form an elastomeric strip without degrading the degradable material. Then, longitudinally-spaced regions of the degradable reinforcing material corresponding to the longitudinally-spaced curved sections of the flange are then degraded, allowing the elastomeric strip to more faithfully follow the curved sections of the flange when the strip is mounted thereon. See also U.S. Pat. No. 5,009,947 Apr. 23, 1991, to McManus et al.
U.S. Pat. No. 4,343,845 Aug. 10, 1982, to Burden et al relates to an elastomeric strip which has a support frame having selected regions of longitudinally displaceable frame portions such as wire loops reinforced by degraded and nondegraded materials that are nondegradable during the frame coating operation for inhibiting longitudinal displacement of the frame portions during the frame coating operation. The degraded material breaks down when the strip is flexed to allow increased flexibility of the strip and the nondegraded material prevents undue elongation or stretching of the strip.
In summary, the manufacture of elastomeric extrusions having wire cores encounter certain difficulties. The neutral geometry of the core must be maintained while it travels through the extruder. After the extrusion leaves the die, it must be provided with sufficient tensile strength to allow pulling through the curing and cooling steps. Furthermore, when applied to a curved flange of a vehicle, the strip must have asymetric geometry to allow bending of the strip around relatively small radius curves.
These issues are addressed by the present invention which provides a variable neutral axis wire core employing relatively low temperature and relatively high temperature threads. Further understanding of the present invention will be had from the accompanying drawings and following disclosure.